This invention generally relates to remote transmitters, such as those used in remote keyless entry systems. More specifically, this invention relates to a remote transmitter having a gain control feature that allows the transmitter to operate at a low power level.
A variety of vehicle security systems are currently available. Typical systems include a remote transmitter that is housed within a key fob so that it can be easily carried about by an individual. With the increasing popularity of such remote transmitters, a variety of difficulties have been presented.
One difficulty to be overcome is the requirement in some parts of the world that remote transmitters operate at relatively low power levels. As one attempts to compensate for lower power levels, other difficulties such as managing gain and harmonics levels are introduced. Additionally, it has proven difficult to make low-power transmitters economically enough to be suitable for mass production. Other difficulties introduced by power level restrictions include maintaining stable performance within a wide temperature range.
This invention addresses the needs that have not been previously met by providing a remote transmitter that generates radio frequency communication signals such as those used in a remote keyless entry system while operating at a relatively low power level.
In general terms this invention is a remote transmitter for use in remote keyless entry systems, for example. The remote transmitter of this invention includes a signal transmitter circuit portion that has an input for receiving data to incorporate into a signal. The signal transmitter circuit portion also includes an output for transmitting a radio frequency signal to a remote receiver. A gain control circuit is coupled with the output of the signal transmitter portion. The gain control circuit includes an inductive load that introduces a frequency that controls gain associated with the signal transmitter portion when generating the transmitted signal. The characteristics of the inductive load are chosen based upon the needs of a particular situation and the characteristics of the components of the signal transmitter circuit portion.
In the preferred embodiment, the signal transmitter portion includes a transistor having a base node, a collector node and an emitter node. The gain control circuit includes a capacitive load coupled between the collector node and the emitter node of the transistor. The inductive load preferably is coupled between the emitter node and ground.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiments. The drawings that accompany the detailed description can be briefly described as follows.